London -LRB- CNN -RRB- -- The security plans for the London Marathon this weekend are being reassessed after the deadly bomb blasts in Boston , London 's Metropolitan Police said Tuesday .

Police and race organizers said they are working closely on security for Sunday 's race .

About 35,000 runners take part in the London Marathon each year , and many more people turn out to cheer them on .

READ MORE : Terror at Boston Marathon : 3 dead , scores wounded

`` We will be reviewing our security arrangements in partnership with London Marathon , '' said event commander Chief Supt. Julia Pendry .

The Metropolitan Police have `` a wealth of experience in policing a wide range of public order events across London , '' she said .

The London Marathon organizers said Tuesday the event `` will go ahead as originally scheduled . ''

`` We have reviewed and will continue to review our security arrangements with the Metropolitan Police and other authorities , '' a statement on the event website said Tuesday .

Chief executive Nick Bitel said : `` We want to reassure our runners , spectators , volunteers and everyone connected with the event that we are doing everything to ensure their safety . ''

The organizers said Monday they were deeply saddened and shocked by the news from Boston . `` Our immediate thoughts are with all the people there and their families . It is a very sad day for athletics and for our friends and colleagues in marathon running , '' they said in a statement .

London is the next , after Boston , of the six races that make up the World Marathon Majors series .

The course , which starts in southeast London , passes through some of the capital 's main business districts before finishing near Buckingham Palace .

More than three-quarters of those taking part will raise money for charity .

` Robust security measures '

`` The bombings in Boston are shocking , cowardly and horrific , and the thoughts of all Londoners this morning will be with the victims , '' London Mayor Boris Johnson said in a statement Tuesday .

`` Boston is a proud city built on history , tradition and a real sense of community . These attacks were aimed at its core , at innocent men , women and children enjoying a spring day out at a major sporting event .

`` We do have robust security measures in place for Sunday 's London Marathon , but given events in Boston it 's only prudent for the police and the organizers of Sunday 's race to reexamine those security arrangements . ''

CNN anchor Piers Morgan tweeted : `` London marathon this Sunday - security at these events will never be the same again . ''

Will Geddes , managing director of threat management company International Corporate Protection , told CNN that it is `` very difficult '' to secure a marathon .

`` You can look at isolating particular areas and trying to secure these -- however , you are looking at a 26-mile-plus route , which often will spread across a major capital , and in terms of protecting it right along the route , it will be very , very difficult , '' he said .

Any potential terrorist `` will be looking for the largest number of casualties they can achieve , so the start point and the finish point will no doubt be two areas the Metropolitan Police will be focusing on and how they can secure those . ''

But , Geddes said , `` to a certain degree , there is only so much they can do . ''

One key element will be the awareness of the general public , which in recent years has played an increasing role in alerting authorities to any suspicious activities or bags left unattended , he added .

A big security operation will also swing into place on Wednesday for the funeral of Margaret Thatcher , Britain 's first woman prime minister .

The Metropolitan Police have said parts of the transport network will be closed down and there will be a large military and police presence on the streets as the funeral procession passes through central London .

Last summer , authorities successfully implemented a huge security plan to keep the city safe during the London Olympics .

READ MORE : Report : 8-year-old boy killed in Boston Marathon blasts identified

READ MORE : Witness : ' I saw blood everywhere '

READ MORE : Apartment searched , but no suspect yet in bombings

CNN 's Antonia Mortensen and Erin McLaughlin contributed to this report .

@highlight

NEW : `` We want to reassure runners , spectators , volunteers '' about safety , says event CEO

@highlight

Organizers of the London Marathon say it will take place as planned Sunday

@highlight

London mayor says `` robust security measures '' are in place for the event

@highlight

Tens of thousands of people take part in the race each year , cheered on by many more